The present invention relates to an array type storage unit system constituting an external storage unit system of a computer system in which collected data such as a file are dispersed to be stored in a plurality of storage units, and more particularly to an array type storage unit system in which increase of the storage units for the purpose of improvement of the data transfer speed, increase of a storage capacity or increase of redundancy is performed dynamically without stop of the system.
Heretofore, as an array type storage unit system, a disk array system is known.
The disk array system is to attain a high-speed data transfer between a control processor and an external storage apparatus by performing input/output operation of a large number of magnetic disk units in parallel in a computer system.
A configuration of the disk array system is described in, for example, a paper of D. Paterson, G. Gibson and R. Katz, "A Case for Redundant Arrays of Inexpensive Disks (RAID)", ACM SIGMOD Conference Proceedings, 1988, pp. 109-116.
The paper proposes a disk array configuration named RAID (Redundant Array of Inexpensive Disks).
The RAID disperses normal input/output data to be stored in a plurality of drives and stores parity data therein.
The parity data is set in order to restore or reconstitute missing data by using the parity data together with a data reconstitution function when the data is lost.
Drives in the disk array system are not increased with a unit of one drive and are increased with a unit of a plurality of drives in which data are dispersed.
In this system, the increased storage area can be treated as a lump of continuous area, so that the mapping information of addresses is merely rewritten and movement of data is not required, to thereby facilitate the adding operation after increase of the storage unit.
That is, the increased storage unit can be added behind the maximum address of the memory area.
In the above paper, however, it seems that increase of drives for changing a width of dispersed data for increase with a unit of one drive and particularly dynamic increase without stop of the system are not described.
As described above while taking the disk array system as an example, the conventional array type storage unit system increases the storage units with a unit of a plurality of storage units in which data are dispersed.
Accordingly, a unit of increased storage units is made larger and it seems that a cost for increase of the storage capacity is increased.
Further, in the conventional array type storage unit system, when the storage units are increased, the number of storage units in which data are dispersed cannot be changed and accordingly there is a possibility that the number of the storage units which operate in parallel upon transfer of data cannot be increased.
Accordingly, there is a possibility that improvement of the data transfer speed due to addition or increase of the storage units cannot be effected.
Furthermore, in the conventional array type storage unit system, in order to increase the storage units with a unit of a plurality of storage units in which data are dispersed, the effect due to the increased redundancy of the storage unit system cannot be expected by only change of mapping of addresses even when new drives are added to the storage units in which data are already stored.